Birds and bees do it, and now so do tiny protein strands — spontaneously moving together in the striking patterns known as collective motion.

Japanese researchers attached filaments of protein to a second protein that acts as a biological motor, rotating and driving the filaments to move. The scientists then injected ATP, a molecule that sends energy flowing within a cell; at first, the filaments meandered aimlessly around. But after about a quarter of an hour, they organized themselves int...